Hybrid stepping motors have been well known for over a quarter of the century as actuators appropriated for highly accurate positioning movements. The hybrid stepping motors are widely used in various machine tools, e.g. with fully automated production lines, as well as computer related instruments including printers, plotters, facsimile machines, and disk drive units.
For increasing the versatility in use, there is made an attempt to minimize the step angle of such a hybrid stepping motor. To this respect, four- and five-phase types of the stepping motor are now commonly provided.
The conventional four- or five-phase stepping motors however have some disadvantages that torque stiffness is unstable, that static torque is varied depending on the stop position, and that the step angle is not at a high accuracy. It is an object of the present invention to eliminate the foregoing disadvantages.